Intra-operative determination of a focal length of a camera for medical applications

ABSTRACT

A method of determining a focal length of a camera and/or of adjusting a viewing direction in a graphical representation of a pre-operative image is provided. The method includes providing uncalibrated camera data of a camera, specifying an initial value of a focal length of the camera, specifying a working distance value of a distance between the camera and the at least part of the tracking system, calculating a distance value of the distance between the camera and the at least part of the tracking system based on the uncalibrated camera data and based on the specified initial value of the focal length of the camera, calculating a change factor based on the specified working distance value and the calculated distance value, and calculating an adapted value of the focal length of the camera based on the initial value of the focal length and based on the change factor.

RELATED APPLICATION DATA

This application is a national phase application of InternationalApplication No. PCT/EP2019/074155 filed Sep. 11, 2019, which claimspriority to International Application No. PCT/EP2018/074664, filed onSep. 12, 2018, the contents of both of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a computer-implemented method, e.g. amedical method, of intra-operatively determining a focal length of acamera. Alternatively or additionally, the present invention relates toa computer-implemented method, e.g. a medical method, for adjusting aviewing direction in a graphical representation of a pre-operativeimage, particularly a three-dimensional image or scan, of at least apart of a patient. The invention further relates to a correspondingcomputer program, a non-transitory program storage medium storing such aprogram and a computer for executing the program, as well as a medicalsystem comprising an electronic data storage device and theaforementioned computer.

TECHNICAL BACKGROUND

In many operating rooms or operating theatres a two-dimensional standardcamera, i.e. a camera not providing three-dimensional or depthinformation, but only acquiring two-dimensional camera data and/ortwo-dimensional images, is arranged, e.g. on a ceiling of the respectiveoperating room. These standard cameras primarily serve to record imagesand/or a video of an operating procedure in order to document theoperating procedure.

Usually, optical characteristics, such as e.g. lens parameters, a focalspot position and/or a value of the focal length (also referred tohereinafter as true or actual value of the focal length), of suchstandard camera of an operating room, are unknown. In other words,standard cameras installed in operating rooms usually provideuncalibrated camera data and/or usually are uncalibrated. Further, adetermination of the optical characteristics usually requires atime-consuming calibration measurement, in which for example the lensparameters, the focal spot position and/or a value of the focal lengthof the respective camera can be determined.

For certain applications, however, such as for example trackingapplications, in which preferably a three-dimensional information can beobtained and/or derived from two-dimensional images of a camera, aninformation about the optical characteristics of the camera may bedesirable.

It may, therefore, be desirable to provide for an improvedcomputer-implemented method for intra-operatively determining a focallength (or a value thereof) of a camera, which camera providesuncalibrated camera data. Likewise, it may be desirable to provide foran improved computer-implemented method for adjusting a viewingdirection in a graphical representation of a pre-operative image of apatient.

The present invention can be used for tracking procedures e.g. inconnection with a system for image-guided surgery such as CURVE, aproduct of Brainlab AG.

Aspects of the present invention, embodiments, examples, exemplaryfeatures and exemplary steps are disclosed in the following. Differentaspects, embodiments, examples, exemplary features and exemplary stepsof the invention can be combined in accordance with the inventionwherever technically expedient and feasible.

EXEMPLARY SHORT DESCRIPTION OF THE INVENTION

In the following, a short description of the specific features of thepresent invention is given which shall not be understood to limit theinvention only to the features or a combination of the featuresdescribed in this section.

The disclosed method relates to a computer-implemented method,particularly a medical method, of intra-operatively determining a focallength of a camera. Alternatively or additionally, the disclosed methodrelates to a computer-implemented method, particularly a medical method,for adjusting a viewing direction in a graphical representation of apre-operative image of at least a part of a patient. Alternatively oradditionally, the disclosed method relates to a computer-implementedmethod, particularly a medical method, of intra-operatively determininga focal length of a camera for adjusting a viewing direction in agraphical representation of a pre-operative image of at least a part ofa patient.

Here and in the following, the term “intra-operatively” may mean thatthe method according to the invention can be performed during and/orsimultaneously to an actual operation and/or surgery performed on apatient.

Further, the “pre-operative image” may refer to three-dimensional imagedata and/or image data set of the at least part of the patient. Forexample, the pre-operative image may be determined in a pre-operativescan using any imaging modality. Accordingly, the pre-operative imagemay refer to a computed tomography (CT) scan or image, a magneticresonance (MR) scan or image, a three-dimensional ultrasound scan orimage, or the like.

The disclosed method comprises providing uncalibrated camera data of acamera, wherein the uncalibrated camera data comprise an image of atracking system. The camera may refer to an uncalibrated camera and/or acamera with unknown optical characteristics, such as e.g. unknown lensparameters, an unknown focal spot position, an unknown optical center,and/or an unknown value of the focal length. Accordingly, the term“uncalibrated camera data” may mean that the optical characteristics ofthe camera are unknown and/or that a reference system of the camera datais unknown.

The method further comprises specifying an initial value of a focallength of the camera and specifying a working distance value of adistance between the camera and the tracking system. Further, the methodcomprises calculating a distance value of the distance between thecamera and the tracking system based on the uncalibrated camera data andbased on the specified initial value of the focal length of the camera.Further, the method comprises calculating a change factor based on thespecified working distance value and the calculated distance value, andcalculating an adapted value of the focal length of the camera based onthe initial value of the focal length and based on the change factor.

Generally, this allows to intra-operatively determine and/or estimatethe value of the focal length of the camera. In turn, this allows toderive further information from the uncalibrated camera data, such ase.g. a three-dimensional information and/or a depth information, as willbe further elucidated in the following.

GENERAL DESCRIPTION OF THE INVENTION

In this section, a description of the general features of the presentinvention is given for example by referring to possible embodiments ofthe invention.

As set out hereinabove, it may be desirable to provide for an improvedcomputer-implemented method for intra-operatively determining a focallength (or a value thereof) of a camera, which camera providesuncalibrated camera data. Likewise, it may be desirable to provide foran improved computer-implemented method for adjusting a viewingdirection in a graphical representation of a pre-operative image of apatient.

This is achieved by the subject-matter of the independent claims,wherein further embodiments are incorporated in the dependent claims andthe following description.

According to a first aspect of the invention, there is provided acomputer-implemented method of intra-operatively determining a focallength and/or a value thereof of a camera and/or for adjusting, e.g.intra-operatively adjusting, a viewing direction in a graphicalrepresentation of a pre-operative image, particularly athree-dimensional image or scan, of at least a part of a patient. Themethod comprises the following steps:

-   -   providing uncalibrated and/or non-calibrated camera data of a        camera, wherein the uncalibrated camera data comprise an image        of at least a part of a tracking system (e.g. positioned close        to a region of interest of the patient), at least a part of a        marker device of the tracking system, at least a part of a        region of interest of the patient and/or at least a part of a        working environment;    -   specifying and/or assuming an initial value of a focal length of        the camera;    -   specifying and/or assuming a working distance value of a        distance between the camera and the at least part of the        tracking system;    -   calculating, computing and/or determining a distance value of        the distance between the camera and the at least part of the        tracking system, e.g. a marker device of the tracking system        (and/or the at least part of the region of interest and/or at        least a part of the working environment), based on the        uncalibrated camera data and based on the specified initial        value of the focal length of the camera;    -   calculating, computing and/or determining a change factor based        on the specified working distance value and the calculated        distance value; and    -   calculating, computing and/or determining an adapted value of        the focal length of the camera based on the initial value of the        focal length and based on the change factor.

As noted above, the camera may be uncalibrated and/or opticalcharacteristics of the camera, particularly a true or actual value ofthe focal length of the camera, may be unknown. By means of theinventive method, particularly by calculating the change factor and/orby calculating the adapted value of the focal length, the true or actualvalue of the focal length may be accurately estimated, approximatedand/or determined. Accordingly, the adapted value of the focal lengthmay represent an estimation and/or approximation of the actual value ofthe focal length. However, the adapted value of the focal length maysubstantially correspond to and/or may substantially be identical to theactual value of the focal length. Generally, determining the adaptedvalue of the focal length substantially corresponding to and/orapproximating the actual value of the focal length may advantageouslyallow to derive comprehensive information from the uncalibrated imagedata, such as for example three-dimensional information of an objectcomprised in the uncalibrated camera (or the respective image),particularly with respect to the camera. For instance, determining theadapted value of the focal length may advantageously allow to determinea relative position of the camera and the object and/or a relativeorientation of the object with respect to the camera.

By way of example, the object may be or refer to at least a part of thetracking system, such as e.g. a marker device of the tracking system.Accordingly, by means of the inventive method, the relative positionand/or orientation of the at least part of the tracking system can beaccurately and precisely determined, although the true or actual valueof the focal length of the camera is unknown. In turn, this allowsutilizing the uncalibrated camera data for a tracking application, inwhich e.g. the relative position and/or orientation of the at least partof the tracking system is determined.

Apart from that, since uncalibrated camera data can be used, thetime-consuming and costly procedure of calibrating the camera in orderto determine the actual focal length can be avoided. In turn, thisallows to retrofit and/or implement the inventive method in operatingrooms and/or operating theatres without requiring modifications toexisting hardware in the respective operating room, particularly withoutrequiring any modification to the camera and/or replacement of thecamera, e.g. by a stereo camera or the like.

The specified and/or assumed initial value of the focal length can bearbitrarily and/or automatically chosen. In other words, the initialvalue may have an arbitrary value and/or may be automatically chosen,e.g. by a computer performing one or more steps of the method. However,the initial value of the focal length may also be chosen from a certaininterval of focal length values, which may represent realistic, expectedand/or potential values of the focal length.

Here and in the following the distance between the camera and the atleast part of the tracking system (and/or the at least a part of themarker device, the at least part of the region of interest and/or atleast a part of a working environment) may refer to an orthogonal and/orshortest distance between the camera and the at least part of thetracking system (and/or the at least a part of the marker device, the atleast part of the region of interest and/or at least a part of a workingenvironment). The orthogonal and/or shortest distance may be measurede.g. along and/or substantially parallel to an optical axis of thecamera. The optical axis of the camera may also be referred to in thefollowing as z-axis. Accordingly, the distance between the camera andthe at least part of the tracking system may be measured between anouter edge of the camera (or a center position of the camera) and anouter edge (or a center position) of the at least part of the trackingsystem, e.g. an outer edge (or center position) of a marker device ofthe tracking system.

Further, the specified and/or assumed working distance value of thedistance between the camera and the at least part of the tracking systemmay refer to an arbitrarily and/or automatically chosen and/or selectedvalue of the distance between the camera and the at least part of thetracking system. In other words, the working distance value may have anarbitrary value and/or may be automatically chosen, e.g. by a computerperforming one or more steps of the method. Accordingly, the assumedworking distance value may differ from an actual or true value of thedistance. Further, the working distance value may be chosen from acertain interval of distance values, which may represent realistic,expected and/or potential values of the distance between the camera andthe at least part of the tracking system. By way of example, the workingdistance value may be selected and/or arbitrarily selected from aninterval of about 0.1 m to about 20 m, particularly from about 0.5 m toabout 10 m, preferably from about 1 m to about 5 m.

The calculated distance value of the distance between the camera and theat least part of the tracking system may be calculated based onprocessing the uncalibrated camera data and based on the initial valueof the focal length. In other words, the calculated distance value maybe derived from the uncalibrated camera data taking into account theinitial value of the focal length. However, for the calculation of thecalculated distance value further image processing techniques mayoptionally be applied or utilized, such as e.g. a point correlationcorrelating certain pixels of the uncalibrated camera data or the like.

Generally, the change factor may refer to and/or denote a change valueand/or a change quantity. Therein, the change factor may be derived fromthe calculated distance value and the specified working distance value.Further, by way of example, the change factor may be multiplied with theinitial value of focal length, added to the initial value, subtractedfrom the initial value or the initial value may be divided by the changefactor in order to calculate the adapted value of the focal length.

It should be noted that the focal length, the initial value of the focallength and/or the adapted value of the focal length may refer to thefocal length, the initial value and/or the adapted value in at least onespatial direction, preferably in two and/or two orthogonal spatialdirections, wherein the at least one spatial direction may be transverseand/or orthogonal to the optical axis of the camera (and/or the z-axis).Particularly, the focal length may refer to a two-dimensional focallength in a first direction and in a second direction, wherein both thefirst and the second directions are transverse and/or orthogonal to az-direction and/or to a direction parallel to the optical axis of thecamera. Further, the first direction may refer to an x-direction and/ormay be orthogonal to the second direction, wherein the second directionmay refer to a y-direction. In other words, the focal length may bemeasured in the first direction and in the second direction in a plane(e.g. an image plane) that is transverse and/or orthogonal to theoptical axis of the camera. Accordingly, the focal length may have afirst component in the first direction and a second component in thesecond direction. Likewise, the initial value of the focal length mayhave a first component in the first direction and a second component inthe second direction. Further, also the adapted value of the focallength may have a first component in the first direction and a secondcomponent in the second direction.

The change factor may refer to a scalar that may be applied to both thefirst component and the second component of the initial value of thefocal length. Alternatively, also the change factor may have a firstcomponent and a second component, wherein the first component of thechange factor may be applied to the first component of the initial valueof the focal length to calculate the first component of the adaptedvalue of the focal length. Similarly, the second component of the changefactor may be applied to the second component of the initial value ofthe focal length to calculate the second component of the adapted valueof the focal length.

Moreover, it should be noted that the inventive method can be performedin real time and/or online during an actual surgery. In other words, themethod can be performed intra-operatively. Accordingly, the camera maycapture and/or acquire a sequence of uncalibrated camera data or datasets, each comprising an image of the at least part of the trackingsystem. For each camera data, each camera data set and/or each image ofthe camera, the method, as described above and in the following, can beperformed, particularly without any delay noticeable by a user and/or asurgeon.

It should be noted, however, that the invention does not involve or inparticular comprise or encompass an invasive step which would representa substantial physical interference with a body of a patient requiringprofessional medical expertise to be carried out and entailing asubstantial health risk even when carried out with the requiredprofessional care and expertise. Particularly, the invention does notinvolve or in particular comprise or encompass any surgical ortherapeutic activity. The invention is instead directed as applicable toimage processing. For this reason alone, no surgical or therapeuticactivity and in particular no surgical or therapeutic step isnecessitated or implied by carrying out the invention.

According to an embodiment of the invention, the camera is a standardoperating room camera. Alternatively or additionally, the camera is atwo-dimensional camera and/or a camera configured to generatetwo-dimensional camera data. Accordingly, the uncalibrated camera datamay refer to two-dimensional data representing, describing and/orcomprising a two-dimensional image of the at least part of the trackingsystem. The camera may, for instance, refer to a standard RGB (Red,Green, Blue) camera. The camera may, for example, be arranged in acenter of an array of light emitting diodes or any other lighting. Suchcamera may be pre-installed in many operating rooms. As noted above,since the true value of the focal length of the camera, which isunknown, can be approximated, estimated and/or determined by means ofthe method according to the present invention, the method can beimplemented and/or retrofit in operating rooms without any modificationto the hardware and/or camera of the respective operating room.

According to an embodiment of the invention, the step of calculating thedistance value and/or the step of computing the change factor comprises:

-   -   determining, computing and/or calculating a deviation of the        calculated distance value with respect to the specified working        distance value; and    -   comparing the determined deviation to a threshold value,        particularly a predetermined and/or pre-set threshold value, for        the deviation of the calculated distance value with respect to        the specified working distance value.

Therein, the deviation of the calculated distance value with respect tothe specified working distance value may be determined based on asubtraction of these two values. Alternatively or additionally a ratioof the calculated distance value and the specified distance value may bedetermined for determining the deviation. Generally, determining thedeviation and comparing this deviation to the threshold value may allowto determine whether the initial value of the focal length should befurther adapted to more closely approximate the true or actual value ofthe camera's focal length. By way of example, the change factor and/orthe adapted focal length value may be calculated if, particularly onlyif, the determined deviation reaches and/or exceeds the threshold value.

According to an embodiment of the invention, at least the followingsteps are repeated in an iteration process:

-   -   calculating, computing and/or determining a distance value of        the distance between the camera and the at least part of the        tracking system based on the uncalibrated camera data and based        on the specified initial value of the focal length of the        camera;    -   calculating, computing and/or determining a change factor based        on the specified working distance value and the calculated        distance value; and    -   calculating, computing and/or determining an adapted value of        the focal length of the camera based on the initial value of the        focal length and based on the change factor.

Optionally, one or more of the following steps may also be repeated inthe iteration process:

-   -   providing uncalibrated and/or non-calibrated camera data of a        camera, wherein the uncalibrated camera data comprise an image        of at least a part of a tracking system, e.g. positioned close        to a region of interest of the patient, (and/or at least a part        of the marker device, at least a part of the region of interest        and/or at least a part of a working environment);    -   specifying and/or assuming an initial value of a focal length of        the camera;    -   specifying and/or assuming a working distance value of a        distance between the camera and the at least part of the        tracking system.

Generally, repeating at least some of the steps of the method in aniteration process may allow to iteratively approximate the true oractual value of the focal length with the adapted value of the focallength. Accordingly, the iteration process may allow to increase anaccuracy and/or precision of the determination, estimation and/orapproximation of the true value of the focal length by the adapted valueof the iteration process.

It should be noted, that the adapted value of the focal length, asdetermined in one iteration of the iteration process, may be used asinitial value of the focal length in a subsequent iteration of theiteration process. Accordingly, as the initial value of the focal lengthmay change in subsequent or consecutive iterations, also the calculateddistance value may change in subsequent or consecutive iterations.Further, the assumed working distance value may be constant in some ofor all the iterations of the iteration process. Alternatively, however,a separate or independent working distance value may be specified foreach iteration of the iteration process.

According to an embodiment of the invention, the iteration process isterminated, if a deviation of the calculated distance value with respectto the specified working distance value reaches and/or falls below athreshold value, particularly a predetermined and/or pre-set thresholdvalue, for the deviation of the calculated distance value with respectto the specified working distance value. Based on such terminationcriterion, a reasonable trade-off between computing time and a precisionor quality, with which the true value of the focal length can beapproximated by the adapted value of the focal length, can be made.

According to an embodiment of the invention, calculating the changefactor comprises calculating a ratio of the specified working distancevalue and the calculated distance value. Alternatively or additionally,the change factor correlates with and/or is indicative of a ratio of thespecified working distance value and the calculated distance value.Accordingly, the change factor may be given by the ratio of thespecified working distance value and the calculated distance value.Alternatively, this ratio may be multiplied by a certain factor and/oran offset may be added to the ratio to calculate the change factor.Generally, the ratio of the specified working distance value and thecalculated distance value may provide an indication about how close theadapted value of the focal length is to the actual value of the focallength.

According to an embodiment of the invention, the method furthercomprises the step of comparing the determined change factor to a clampfactor, wherein the clamp factor is indicative of a maximum allowedvalue of the change factor, particularly a maximum allowed value of thechange factor for a single iteration and/or each iteration of theiteration process. Accordingly, the clamp factor may relate to athreshold value indicative of the maximum allowed value of the changefactor for a single iteration and/or each iteration of the iterationprocess.

According to an embodiment of the invention, the method furthercomprises the step of reducing the change factor if the determinedchange factor reaches and/or exceeds the clamp factor. Therein, thechange factor may be reduced by a predetermined, pre-set and/orspecifiable amount and/or percentage. Further, the change factor may bereduced in a single and/or each iteration of the iteration process, ifthe determined change factor reaches and/or exceeds the clamp factor inthe respective iteration.

Generally, by using and/or applying the clamp factor and/or thecorresponding reduction of the change factor, the maximum change of thevalue of the focal length, i.e. the maximum change of the adapted valueof the focal length with respect to the initial value, may be limited,e.g. for a single and/or each iteration of the iteration process. Whenusing the adapted value of the focal length for further purposes or afurther application, such as e.g. for adjusting the viewing direction inthe graphical representation of the pre-operative image, as described inmore detail hereinafter, a restriction of the maximum change periteration may ensure smooth transitions between various viewingdirections. This may increase a comfort in visual perception for a user.

According to an embodiment of the invention, the tracking systemcomprises a marker device with one or more surfaces, e.g. one or moresubstantially flat surfaces, wherein at least one optical marker,preferably a plurality of optical markers, is arranged on the one ormore surfaces of the marker device. Different surfaces of the markerdevice, e.g. at least two surfaces of the marker device, may be arrangedtransverse and/or orthogonal to each other. In other words, therespective surface normal vectors of at least two surfaces may betransverse and/or orthogonal to each other. The one or more markers maybe monochromatic markers. Further, one or more of the markers may have acertain pattern and/or code. For example, one or more of the markers maycomprise an optical pattern, e.g. similar to a quick response (QR) code.On each surface, at least one marker, preferably at least two or threemarkers, even more preferably at least four markers, for example four tofive markers, may be arranged. This may allow to increase a stability ofa tracking of the marker device and/or of the markers arranged thereon.Generally, the marker device may be arbitrarily shaped, such as e.g.box-like, rectangular, polygonal, cuboidal, and/or trapezoidal. Further,the marker device may be arranged on and/or attached to an instrument,such as e.g. a surgical instrument. Accordingly, the marker device maybe configured and/or arranged to be moved, particularly manually moved,by a user, e.g. a medical doctor during a surgery.

For tracking purposes, it may be sufficient that the marker devicecomprises at least one marker on at least one surface of the markerdevice, wherein a geometry of the marker may preferably be known. If aplurality of markers is arranged on the marker device, a geometry ofeach of the markers and/or a geometry of the markers with respect toeach other may be known and/or pre-determined.

According to an embodiment of the invention, the method furthercomprises the following steps:

-   -   detecting one or more optical markers arranged on one or more        surfaces of a marker device of the tracking system based on the        adapted focal length value and based on the uncalibrated camera        data; and    -   determining a position of a reference point of the marker        device, particularly a position of a tip of the marker device,        with respect to and/or relative to the camera (and/or a position        of the camera). Alternatively or additionally an orientation of        the marker device of the tracking system with respect to the        camera (and/or a position of the camera) may be determined.

Generally, by using the adapted focal length value for detecting the oneor more optical markers a precision, stability and/or reliability of thedetection of the one or more markers may be increased. Further, usingthe adapted focal length may allow to use the uncalibrated camera datawithout knowing the actual optical properties of the camera,particularly the actual value of the focal length. In turn, this allowsretrofitting the inventive method to existing hardware in an operatingroom, thereby significantly reducing installation cost and/or effort.

It should be noted that a plurality of optical markers can be detectedsubstantially simultaneously. This may further allow increasing astability, reliability and/or precision of the determination of thereference point of the marker device and/or the orientation of themarker device with respect to the camera.

Therein, the reference point of the marker device may refer to anarbitrary reference point of the marker device, such as e.g. an edge, aborder and/or a tip of the marker device, relative to the position ofthe camera. Such reference points may be determined with high accuracyand/or precision. Further, the determined reference point may refer to apoint in three-dimensional space in an arbitrary coordinate or referencesystem, e.g. in which the position of the camera is known. The positionof the camera may refer to a reference position of the camera, such as,e.g. an edge and/or a center of the camera. Accordingly, the determinedreference point may be given in and/or may comprise three spatialcoordinates relative to the position of the camera.

Further, the orientation of the marker device of the tracking systemwith respect to the camera may refer to an orientation of an axis of themarker device, e.g. a longitudinal axis, and/or any other geometricalfeature of the marker device, such as e.g. an edge, with respect to thecamera and/or with respect to the position of the camera. Theorientation of the marker device may be given as a vector inthree-dimensional space in an arbitrary coordinate or reference system,e.g. in which the position of the camera is known.

According to an embodiment of the invention, the method furthercomprises the steps of determining tracking data of the tracking systemand/or the marker device based on the detected one or more opticalmarkers of the tracking system, wherein the tracking data are indicativeof and/or comprise information about a position of the reference pointof the marker device with respect to the camera and/or the position ofthe camera. Alternatively or additionally, the tracking data areindicative of and/or comprise information about the determinedorientation of the marker device of the tracking system with respect tothe camera and/or the camera.

According to an embodiment of the invention, the method furthercomprises:

-   -   displaying, on a graphical user interface and/or a display, a        graphical representation of a pre-operative image of at least a        part of the patient; and    -   adjusting a viewing direction of the graphical representation of        the pre-operative image based on the determined position of the        reference point of the marker device and/or based on the        determined orientation of the marker device with respect to the        camera.

Therein, pre-operative image may refer to a three-dimensional image,three-dimensional image data and/or a three-dimensional image data setof the at least part of the patient. The pre-operative image may bedetermined in a pre-operative scan of the patient using any suitableimaging modality. For instance, the pre-operative image may refer to acomputed tomography (CT) scan or image, a magnetic resonance (MR) scanor image, a three-dimensional ultrasound scan or image, or the like.

Further, the viewing direction may refer to a direction of a virtualview in the graphical representation of the pre-operative image asdisplayed on the graphical user interface. Therein, the viewingdirection may be centered on a part or body part of the patient and/oron a center of view. The center of view may be defined by and/or may bederived from the determined position of the reference point of themarker device. Apart from that, the viewing direction may be defined byand/or may be derived from the determined orientation of the markerdevice.

Generally, adjusting the viewing direction of the graphicalrepresentation of the pre-operative image based on the determinedposition and/or orientation of the marker device may allow a user tointeractively change and/or adapt the viewing direction and/or thecenter of view in the graphical representation by moving, translatingand/or rotating the marker device, e.g. manually. Accordingly, the usermay not have to navigate through the graphical representation byactuating any actuating element, e.g. on the graphical user interface.This may be particularly advantageous in view of clinical hygienicstandards. Also, an efficiency of a process of navigating through thepre-operative image or the graphical representation thereof may besignificantly increased, e.g. when compared to a situation, where thenavigation is done by actuating an actuating element, e.g. on thegraphical user interface. This may further safe time in the overallprocedure, e.g. a surgery, that the user may have to perform on thepatient.

According to an embodiment of the invention, the viewing direction ofthe graphical representation is adjusted according and/or correspondingto the orientation of the marker device with respect to the camera. Byway of example, a vector describing the orientation of the marker deviceand/or tracking data indicative of the orientation of the marker devicemay be used to derive and/or may define the viewing direction in thegraphical representation. Accordingly, the viewing direction in thegraphical representation may correlate with the determined orientationof the marker device. In other words, the determined orientation of themarker device may be translated to the viewing direction. Therein, thegraphical representation may be displayed along this viewing direction.

According to an embodiment of the invention, the method furthercomprises:

-   -   providing further uncalibrated camera data of the camera,        wherein the further uncalibrated camera data comprise a further        image of the at least part of the tracking system;    -   detecting the one or more optical markers of the marker device        of the tracking system based on the further uncalibrated camera        data;    -   determining a further orientation of the marker device of the        tracking system with respect to the camera based on the further        uncalibrated camera data; and    -   determining an orientation change of the marker device, the        orientation change being indicative of a change of the further        orientation of the marker device, as determined based on the        further uncalibrated camera data, with respect to the determined        orientation of the marker device, as determined based on the        uncalibrated camera data.

The uncalibrated camera data and the further uncalibrated camera datamay each refer to an image captured and/or acquired by the camera at twodifferent instants of time. Accordingly, the uncalibrated camera datamay be acquired at a first time and the further uncalibrated may beacquired at a second time, which differs from the first time. In otherwords, the uncalibrated camera data and the further uncalibrated cameradata may refer to a sequence and/or time-series of images (oruncalibrated camera data) as acquired and/or captured by the camera. Theorientation of the marker device may change between the first time andthe second (and/or between the uncalibrated camera data and the furtheruncalibrated camera data), e.g. due to a movement, translation and/orrotation of the marker device by the user. The orientation change and/orchange in the orientation of the marker device may then be determinedand e.g. subsequently used for adjusting the viewing direction in thegraphical representation. Generally, the orientation change may bedetermined e.g. based on a ratio and/or a difference of the orientationof the orientation and the further orientation of the marker device. Byway of example, the orientation change may be indicative of and/orcorrelate with a movement and/or rotation of the marker device by acertain angle.

According to an embodiment of the invention, the method furthercomprises the step of translating the determined orientation change ofthe marker device into a viewing change of the viewing direction of thegraphical representation of the pre-operative image. Accordingly, basedon the determined orientation change, the viewing change in thegraphical representation may be determined and/or calculated. By way ofexample, a movement and/or rotation of the marker device by a certainangle, as described by the orientation change, may be translated intothe viewing change, which may be indicative of and/or correlate with achange of the viewing angle in the graphical representation.

According to an embodiment of the invention, the determined orientationchange is translated into the viewing change based on weighting thedetermined orientation change with a weighting factor, such that theviewing change is increased or decreased relative to the orientationchange. Accordingly, by means of the weighting factor, the orientationchange may be amplified or mitigated to provide the viewing change.Thus, the weighting factor may serve to adapt a sensitivity of anadjustment of the viewing direction in response to a movement and/orrotation of the marker device. By way of example, a movement/rotation ofthe marker device by a first angle may be translated, by applying theweighting factor, e.g. by multiplying the orientation change with theweighting factor, into a viewing angle corresponding to a second anglelarger than the first angle. In other words, a small movement/rotationof the marker device may cause a large change of the viewing direction.This allows e.g. to change the viewing direction by an angle of up toand even more than about 180° by rotating the marker device by less thanabout 180°. Alternatively, a movement/rotation of the marker device by afirst angle may be translated, by applying the weighting factor, e.g. bymultiplying the orientation change with the weighting factor, into aviewing angle corresponding to a second angle less than the first angle.Accordingly, a large movement/rotation of the marker device may cause asmall change of the viewing direction. This may allow to preciselyadjust the viewing direction by means of moving/rotating the markerdevice. Overall, the weighting factor may allow to control that arotation/movement of the marker device can cause a subtle or strongrotation in the graphical representation and/or in a virtual view of thepre-operative image. By way of example, a value of the weighting factormay be specifiable and/or adjustable by the user, e.g. by actuating aslider on a graphical user interface.

According to an embodiment of the invention, the method furthercomprises the step of registering a longitudinal axis of the patientbased on pointing, e.g. sequentially pointing, at least a part of thetracking system, particularly a marker device of the tracking system, toat least two longitudinal points on the patient, wherein the at leasttwo longitudinal points are spaced apart from each other in a directionparallel to the longitudinal axis of the patient. Alternatively oradditionally, the method further comprises the step of registering atransverse axis of the patient based on pointing, e.g. sequentiallypointing, at least a part of the tracking system, particularly a markerdevice of the tracking system, to at least two transverse points on thepatient, wherein the at least two transverse points are spaced apartfrom each other in a direction parallel to the transverse axis of thepatient. Such registration of the longitudinal and/or the transverseaxis of the patient may serve to determine the main directions of thepatient, e.g. the four main directions, i.e. top, bottom, left, right.This may allow to adjust and/or align an overall orientation of thepre-operative image with respect to the longitudinal and/or transverseaxis of the patient. It should be noted that the registration of thelongitudinal and/or the transverse axis may be performed once, e.g.prior to an actual surgery. By way of example, the marker device and/oran instrument, on which the marker device may be arranged, may bepointed to four points on the patient's skin, wherein those four pointsmay form and/or define the main directions of the patient. Further, theregistration of the longitudinal and/or transverse axis may be bound topatient reference of the tracking system, which patient reference may bearranged close to and/or nearby the patient, e.g. at a fixed positionrelative to the patient. This allows to detect and/or compensatemovements of the patient during a surgery and to adapt the graphicalrepresentation accordingly, e.g. if the patient is shifted during thesurgery by moving the couch or patient support, on which the patient maybe arranged. Therein, the patient reference of the tracking system maycomprise at least one surface, e.g. a substantially flat surface, and/orat least one optical marker.

In a second aspect, the invention is directed to a program, programelement and/or a computer program which, when running on at least oneprocessor (for example, a processor) of at least one computer (forexample, a computer), when running on a computer, or when loaded onto acomputer, e.g. into at least one memory (for example, a memory) of atleast one computer (for example, a computer), causes the at least onecomputer to perform the method according to the first aspect, asdescribed above and in the following.

The invention may alternatively or additionally relate to a (physical,for example electrical, for example technically generated) signal wave,for example a digital signal wave, carrying information which representsthe program, for example the aforementioned program, which for examplecomprises code means which are adapted to perform any or all of thesteps of the method according to the first aspect, as described aboveand in the following.

A computer program stored on a disc is a data file, and when the file isread out and transmitted it becomes a data stream for example in theform of a (physical, for example electrical, for example technicallygenerated) signal. The signal can be implemented as the signal wavewhich is described herein. For example, the signal, for example thesignal wave is constituted to be transmitted via a computer network, forexample LAN, WLAN, WAN, for example the internet. The inventionaccording to the second aspect therefore may alternatively oradditionally relate to a data stream representative of theaforementioned program.

In a third aspect, the invention is directed to a non-transitorycomputer-readable program storage medium on which the program accordingto the second aspect is stored.

In a fourth aspect, the invention is directed to at least one computer(for example, a computer), comprising at least one processor (forexample, a processor) and at least one memory (for example, a memory),wherein the program according to the second aspect is running on theprocessor or is loaded into the memory, or wherein the at least onecomputer comprises the computer-readable program storage mediumaccording to the third aspect.

In a fifth aspect, the invention is directed to a medical system,comprising:

-   -   a) the at least one computer according to the fourth aspect;    -   b) at least one electronic data storage device storing at least        the uncalibrated camera data; and    -   c) a medical device for carrying out a medical procedure on the        patient,        -   wherein the at least one computer is operably coupled to    -   the at least one electronic data storage device for acquiring,        from the at least one data storage device, at least the        uncalibrated camera data, and    -   the medical device for issuing a control signal to the medical        device for controlling the operation of the medical device, e.g.        on the basis of the uncalibrated camera data and/or the adapted        value of the focal length, as described above and in the        following.

According to an embodiment of the invention, the medical devicecomprises a graphical user interface for displaying a graphicalrepresentation of a pre-operative image of at least a part of thepatient, wherein the at least one computer is operably coupled to thegraphical user interface for controlling a viewing direction of thegraphical representation based on the calculated adapted value of thefocal length of the camera.

The present invention also relates to the use of any of the first tofifth aspect. Particularly, the invention also relates to the use of themethod according to the first aspect, the program according to thesecond aspect, the computer-readable medium according to the thirdaspect and/or the computer according to the fourth aspect in the medicalsystem or any embodiment thereof according to the fifth aspect.

It is emphasized that features, functions, elements and/or steps, whichare described above and in the following with reference to one aspect ofthe invention, equally apply to any other aspect of the inventiondescribed above and in the following. Particularly, features and/orsteps, as described above and in the following with reference to themethod according to the first aspect, equally apply the computer programaccording to the second aspect, to the computer-readable mediumaccording to the third aspect, to the computer according to the fourthaspect and/or to the medical system according to the fifth aspect, andvice versa.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

DEFINITIONS

In this section, definitions for specific terminology used in thisdisclosure are provided which also form part of the present disclosure.

Computer Implemented Method

The method in accordance with the invention is for example a computerimplemented method. For example, all the steps or merely some of thesteps (i.e. less than the total number of steps) of the method inaccordance with the invention can be executed by a computer (forexample, at least one computer). An embodiment of the computerimplemented method is a use of the computer for performing a dataprocessing method. An embodiment of the computer implemented method is amethod concerning the operation of the computer such that the computeris operated to perform one, more or all steps of the method.

The computer for example comprises at least one processor and forexample at least one memory in order to (technically) process the data,for example electronically and/or optically. The processor being forexample made of a substance or composition which is a semiconductor, forexample at least partly n- and/or p-doped semiconductor, for example atleast one of II-, III-, IV-, V-, VI-semiconductor material, for example(doped) silicon and/or gallium arsenide. The calculating or determiningsteps described are for example performed by a computer. Determiningsteps or calculating steps are for example steps of determining datawithin the framework of the technical method, for example within theframework of a program. A computer is for example any kind of dataprocessing device, for example electronic data processing device. Acomputer can be a device which is generally thought of as such, forexample desktop PCs, notebooks, netbooks, etc., but can also be anyprogrammable apparatus, such as for example a mobile phone or anembedded processor. A computer can for example comprise a system(network) of “sub-computers”, wherein each sub-computer represents acomputer in its own right. The term “computer” includes a cloudcomputer, for example a cloud server. The term “cloud computer” includesa cloud computer system which for example comprises a system of at leastone cloud computer and for example a plurality of operativelyinterconnected cloud computers such as a server farm. Such a cloudcomputer is preferably connected to a wide area network such as theworld wide web (WWW) and located in a so-called cloud of computers whichare all connected to the world wide web. Such an infrastructure is usedfor “cloud computing”, which describes computation, software, dataaccess and storage services which do not require the end user to knowthe physical location and/or configuration of the computer delivering aspecific service. For example, the term “cloud” is used in this respectas a metaphor for the Internet (world wide web). For example, the cloudprovides computing infrastructure as a service (IaaS). The cloudcomputer can function as a virtual host for an operating system and/ordata processing application which is used to execute the method of theinvention. The cloud computer is for example an elastic compute cloud(EC2) as provided by Amazon Web Services™. A computer for examplecomprises interfaces in order to receive or output data and/or performan analogue-to-digital conversion. The data are for example data whichrepresent physical properties and/or which are generated from technicalsignals. The technical signals are for example generated by means of(technical) detection devices (such as for example devices for detectingmarker devices) and/or (technical) analytical devices (such as forexample devices for performing (medical) imaging methods), wherein thetechnical signals are for example electrical or optical signals. Thetechnical signals for example represent the data received or outputtedby the computer. The computer is preferably operatively coupled to adisplay device which allows information outputted by the computer to bedisplayed, for example to a user. One example of a display device is avirtual reality device or an augmented reality device (also referred toas virtual reality glasses or augmented reality glasses) which can beused as “goggles” for navigating. A specific example of such augmentedreality glasses is Google Glass (a trademark of Google, Inc.). Anaugmented reality device or a virtual reality device can be used both toinput information into the computer by user interaction and to displayinformation outputted by the computer. Another example of a displaydevice would be a standard computer monitor comprising for example aliquid crystal display operatively coupled to the computer for receivingdisplay control data from the computer for generating signals used todisplay image information content on the display device. A specificembodiment of such a computer monitor is a digital lightbox. An exampleof such a digital lightbox is Buzz®, a product of Brainlab AG. Themonitor may also be the monitor of a portable, for example handheld,device such as a smart phone or personal digital assistant or digitalmedia player.

The invention also relates to a program which, when running on acomputer, causes the computer to perform one or more or all of themethod steps described herein and/or to a program storage medium onwhich the program is stored (in particular in a non-transitory form)and/or to a computer comprising said program storage medium and/or to a(physical, for example electrical, for example technically generated)signal wave, for example a digital signal wave, carrying informationwhich represents the program, for example the aforementioned program,which for example comprises code means which are adapted to perform anyor all of the method steps described herein.

Within the framework of the invention, computer program elements can beembodied by hardware and/or software (this includes firmware, residentsoftware, micro-code, etc.). Within the framework of the invention,computer program elements can take the form of a computer programproduct which can be embodied by a computer-usable, for examplecomputer-readable data storage medium comprising computer-usable, forexample computer-readable program instructions, “code” or a “computerprogram” embodied in said data storage medium for use on or inconnection with the instruction-executing system. Such a system can be acomputer; a computer can be a data processing device comprising meansfor executing the computer program elements and/or the program inaccordance with the invention, for example a data processing devicecomprising a digital processor (central processing unit or CPU) whichexecutes the computer program elements, and optionally a volatile memory(for example a random access memory or RAM) for storing data used forand/or produced by executing the computer program elements. Within theframework of the present invention, a computer-usable, for examplecomputer-readable data storage medium can be any data storage mediumwhich can include, store, communicate, propagate or transport theprogram for use on or in connection with the instruction-executingsystem, apparatus or device. The computer-usable, for examplecomputer-readable data storage medium can for example be, but is notlimited to, an electronic, magnetic, optical, electromagnetic, infraredor semiconductor system, apparatus or device or a medium of propagationsuch as for example the Internet. The computer-usable orcomputer-readable data storage medium could even for example be paper oranother suitable medium onto which the program is printed, since theprogram could be electronically captured, for example by opticallyscanning the paper or other suitable medium, and then compiled,interpreted or otherwise processed in a suitable manner. The datastorage medium is preferably a non-volatile data storage medium. Thecomputer program product and any software and/or hardware described hereform the various means for performing the functions of the invention inthe example embodiments. The computer and/or data processing device canfor example include a guidance information device which includes meansfor outputting guidance information. The guidance information can beoutputted, for example to a user, visually by a visual indicating means(for example, a monitor and/or a lamp) and/or acoustically by anacoustic indicating means (for example, a loudspeaker and/or a digitalspeech output device) and/or tactilely by a tactile indicating means(for example, a vibrating element or a vibration element incorporatedinto an instrument). For the purpose of this document, a computer is atechnical computer which for example comprises technical, for exampletangible components, for example mechanical and/or electroniccomponents. Any device mentioned as such in this document is a technicaland for example tangible device.

Acquiring Data

According to the present disclosure, the terms acquiring data andretrieving data may be used synonymously. The expression “acquiringdata” for example encompasses (within the framework of a computerimplemented method) the scenario in which the data are determined by thecomputer implemented method or program. Determining data for exampleencompasses measuring physical quantities and transforming the measuredvalues into data, for example digital data, and/or computing (and e.g.outputting) the data by means of a computer and for example within theframework of the method in accordance with the invention. The meaning of“acquiring data” also for example encompasses the scenario in which thedata are received or retrieved by (e.g. input to) the computerimplemented method or program, for example from another program, aprevious method step or a data storage medium, for example for furtherprocessing by the computer implemented method or program. Generation ofthe data to be acquired may but need not be part of the method inaccordance with the invention. The expression “acquiring data” cantherefore also for example mean waiting to receive data and/or receivingthe data. The received data can for example be inputted via aninterface. The expression “acquiring data” can also mean that thecomputer implemented method or program performs steps in order to(actively) receive or retrieve the data from a data source, for instancea data storage medium (such as for example a ROM, RAM, database, harddrive, etc.), or via the interface (for instance, from another computeror a network). The data acquired by the disclosed method or device,respectively, may be acquired from a database located in a data storagedevice which is operably to a computer for data transfer between thedatabase and the computer, for example from the database to thecomputer. The computer acquires the data for use as an input for stepsof determining data. The determined data can be output again to the sameor another database to be stored for later use. The database or databaseused for implementing the disclosed method can be located on networkdata storage device or a network server (for example, a cloud datastorage device or a cloud server) or a local data storage device (suchas a mass storage device operably connected to at least one computerexecuting the disclosed method). The data can be made “ready for use” byperforming an additional step before the acquiring step. In accordancewith this additional step, the data are generated in order to beacquired. The data are for example detected or captured (for example byan analytical device). Alternatively or additionally, the data areinputted in accordance with the additional step, for instance viainterfaces. The data generated can for example be inputted (for instanceinto the computer). In accordance with the additional step (whichprecedes the acquiring step), the data can also be provided byperforming the additional step of storing the data in a data storagemedium (such as for example a ROM, RAM, CD and/or hard drive), such thatthey are ready for use within the framework of the method or program inaccordance with the invention. The step of “acquiring data” cantherefore also involve commanding a device to obtain and/or provide thedata to be acquired. In particular, the acquiring step does not involvean invasive step which would represent a substantial physicalinterference with the body, requiring professional medical expertise tobe carried out and entailing a substantial health risk even when carriedout with the required professional care and expertise. In particular,the step of acquiring data, for example determining data, does notinvolve a surgical step and in particular does not involve a step oftreating a human or animal body using surgery or therapy. In order todistinguish the different data used by the present method, the data aredenoted (i.e. referred to) as “XY data” and the like and are defined interms of the information which they describe, which is then preferablyreferred to as “XY information” and the like.

Registering

The n-dimensional image of a body is registered when the spatiallocation of each point of an actual object within a space, for example abody part in an operating theatre, is assigned an image data point of animage (CT, MR, etc.) stored in a navigation system.

Image Registration

Image registration is the process of transforming different sets of datainto one co-ordinate system. The data can be multiple photographs and/ordata from different sensors, different times or different viewpoints. Itis used in computer vision, medical imaging and in compiling andanalysing images and data from satellites. Registration is necessary inorder to be able to compare or integrate the data obtained from thesedifferent measurements.

Marker

It is the function of a marker (e.g. an optical marker) to be detectedby a marker detection device (for example, a camera or an ultrasoundreceiver or analytical devices such as CT or MRI devices) in such a waythat its spatial position (i.e. its spatial location and/or alignment)can be ascertained. The detection device is for example part of anavigation system. The markers can be active markers. An active markercan for example emit electromagnetic radiation and/or waves which can bein the infrared, visible and/or ultraviolet spectral range. A marker canalso however be passive, i.e. can for example reflect electromagneticradiation in the infrared, visible and/or ultraviolet spectral range orcan block x-ray radiation. To this end, the marker can be provided witha surface which has corresponding reflective properties or can be madeof metal in order to block the x-ray radiation. It is also possible fora marker to reflect and/or emit electromagnetic radiation and/or wavesin the radio frequency range or at ultrasound wavelengths. A markerpreferably has a spherical and/or spheroid shape and can therefore bereferred to as a marker sphere; markers can however also exhibit acornered, for example cubic, shape.

Marker Device

A marker device can for example be a reference star or a pointer or asingle marker or a plurality of (individual) markers which are thenpreferably in a predetermined spatial relationship. A marker devicecomprises one, two, three or more markers, wherein two or more suchmarkers are in a predetermined spatial relationship. This predeterminedspatial relationship is for example known to a navigation system and isfor example stored in a computer of the navigation system.

In another embodiment, a marker device comprises an optical pattern, forexample on a two-dimensional surface. The optical pattern might comprisea plurality of geometric shapes like circles, rectangles and/ortriangles. The optical pattern can be identified in an image captured bya camera, and the position of the marker device relative to the cameracan be determined from the size of the pattern in the image, theorientation of the pattern in the image and the distortion of thepattern in the image. This allows determining the relative position inup to three rotational dimensions and up to three translationaldimensions from a single two-dimensional image.

The position of a marker device can be ascertained, for example by amedical navigation system. If the marker device is attached to anobject, such as a bone or a medical instrument, the position of theobject can be determined from the position of the marker device and therelative position between the marker device and the object. Determiningthis relative position is also referred to as registering the markerdevice and the object. The marker device or the object can be tracked,which means that the position of the marker device or the object isascertained twice or more over time.

Marker Holder

A marker holder is understood to mean an attaching device for anindividual marker which serves to attach the marker to an instrument, apart of the body and/or a holding element of a reference star, whereinit can be attached such that it is stationary and advantageously suchthat it can be detached. A marker holder can for example be rod-shapedand/or cylindrical. A fastening device (such as for instance a latchingmechanism) for the marker device can be provided at the end of themarker holder facing the marker and assists in placing the marker deviceon the marker holder in a force fit and/or positive fit.

Pointer

A pointer is a rod which comprises one or more—advantageously,two—markers fastened to it and which can be used to measure offindividual co-ordinates, for example spatial co-ordinates (i.e.three-dimensional co-ordinates), on a part of the body, wherein a userguides the pointer (for example, a part of the pointer which has adefined and advantageously fixed position with respect to the at leastone marker attached to the pointer) to the position corresponding to theco-ordinates, such that the position of the pointer can be determined byusing a surgical navigation system to detect the marker on the pointer.The relative location between the markers of the pointer and the part ofthe pointer used to measure off co-ordinates (for example, the tip ofthe pointer) is for example known. The surgical navigation system thenenables the location (of the three-dimensional co-ordinates) to beassigned to a predetermined body structure, wherein the assignment canbe made automatically or by user intervention.

Navigation System

The present invention is also directed to a navigation system forcomputer-assisted surgery. This navigation system preferably comprisesthe aforementioned computer for processing the data provided inaccordance with the computer implemented method as described in any oneof the embodiments described herein. The navigation system preferablycomprises a detection device for detecting the position of detectionpoints which represent the main points and auxiliary points, in order togenerate detection signals and to supply the generated detection signalsto the computer, such that the computer can determine the absolute mainpoint data and absolute auxiliary point data on the basis of thedetection signals received. A detection point is for example a point onthe surface of the anatomical structure which is detected, for exampleby a pointer. In this way, the absolute point data can be provided tothe computer. The navigation system also preferably comprises a userinterface for receiving the calculation results from the computer (forexample, the position of the main plane, the position of the auxiliaryplane and/or the position of the standard plane). The user interfaceprovides the received data to the user as information. Examples of auser interface include a display device such as a monitor, or aloudspeaker. The user interface can use any kind of indication signal(for example a visual signal, an audio signal and/or a vibrationsignal). One example of a display device is an augmented reality device(also referred to as augmented reality glasses) which can be used asso-called “goggles” for navigating. A specific example of such augmentedreality glasses is Google Glass (a trademark of Google, Inc.). Anaugmented reality device can be used both to input information into thecomputer of the navigation system by user interaction and to displayinformation outputted by the computer.

The invention also relates to a navigation system for computer-assistedsurgery, comprising:

a computer for processing the absolute point data and the relative pointdata;

a detection device for detecting the position of the main and auxiliarypoints in order to generate the absolute point data and to supply theabsolute point data to the computer;

a data interface for receiving the relative point data and for supplyingthe relative point data to the computer; and

a user interface for receiving data from the computer in order toprovide information to the user, wherein the received data are generatedby the computer on the basis of the results of the processing performedby the computer.

Surgical Navigation System

A navigation system, such as a surgical navigation system, is understoodto mean a system which can comprise: at least one marker device; atransmitter which emits electromagnetic waves and/or radiation and/orultrasound waves; a receiver which receives electromagnetic waves and/orradiation and/or ultrasound waves; and an electronic data processingdevice which is connected to the receiver and/or the transmitter,wherein the data processing device (for example, a computer) for examplecomprises a processor (CPU) and a working memory and advantageously anindicating device for issuing an indication signal (for example, avisual indicating device such as a monitor and/or an audio indicatingdevice such as a loudspeaker and/or a tactile indicating device such asa vibrator) and a permanent data memory, wherein the data processingdevice processes navigation data forwarded to it by the receiver and canadvantageously output guidance information to a user via the indicatingdevice. The navigation data can be stored in the permanent data memoryand for example compared with data stored in said memory beforehand.

Imaging Methods

In the field of medicine, imaging methods (also called imagingmodalities and/or medical imaging modalities) are used to generate imagedata (for example, two-dimensional or three-dimensional image data) ofanatomical structures (such as soft tissues, bones, organs, etc.) of thehuman body. The term “medical imaging methods” is understood to mean(advantageously apparatus-based) imaging methods (for example so-calledmedical imaging modalities and/or radiological imaging methods) such asfor instance computed tomography (CT) and cone beam computed tomography(CBCT, such as volumetric CBCT), x-ray tomography, magnetic resonancetomography (MRT or MRI), conventional x-ray, sonography and/orultrasound examinations, and positron emission tomography. For example,the medical imaging methods are performed by the analytical devices.Examples for medical imaging modalities applied by medical imagingmethods are: X-ray radiography, magnetic resonance imaging, medicalultrasonography or ultrasound, endoscopy,elastography, tactile imaging,thermography, medical photography and nuclear medicine functionalimaging techniques as positron emission tomography (PET) andSingle-photon emission computed tomography (SPECT), as mentioned byWikipedia.

The image data thus generated is also termed “medical imaging data”.Analytical devices for example are used to generate the image data inapparatus-based imaging methods. The imaging methods are for exampleused for medical diagnostics, to analyse the anatomical body in order togenerate images which are described by the image data. The imagingmethods are also for example used to detect pathological changes in thehuman body. However, some of the changes in the anatomical structure,such as the pathological changes in the structures (tissue), may not bedetectable and for example may not be visible in the images generated bythe imaging methods. A tumour represents an example of a change in ananatomical structure. If the tumour grows, it may then be said torepresent an expanded anatomical structure. This expanded anatomicalstructure may not be detectable; for example, only a part of theexpanded anatomical structure may be detectable. Primary/high-gradebrain tumours are for example usually visible on MRI scans when contrastagents are used to infiltrate the tumour. MRI scans represent an exampleof an imaging method. In the case of MRI scans of such brain tumours,the signal enhancement in the MRI images (due to the contrast agentsinfiltrating the tumour) is considered to represent the solid tumourmass. Thus, the tumour is detectable and for example discernible in theimage generated by the imaging method. In addition to these tumours,referred to as “enhancing” tumours, it is thought that approximately 10%of brain tumours are not discernible on a scan and are for example notvisible to a user looking at the images generated by the imaging method.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described with reference to theappended figures which give background explanations and representspecific embodiments of the invention. The scope of the invention ishowever not limited to the specific features disclosed in the context ofthe figures, wherein

FIG. 1 shows a flowchart illustrating steps of a method of determining afocal length of a camera and/or of adjusting a viewing direction in agraphical representation of a pre-operative image of at least a part ofa patient according to an exemplary embodiment of the invention;

FIG. 2 schematically shows a medical system according to an exemplaryembodiment of the invention;

FIG. 3 shows a medical system according to another exemplary embodimentof the invention;

FIG. 4 shows a marker device of the medical system of FIG. 3 ;

FIG. 5 shows a flowchart illustrating steps of a method of determining afocal length of a camera and/or of adjusting a viewing direction in agraphical representation of a pre-operative image of at least a part ofa patient according to an exemplary embodiment of the invention;

FIG. 6 shows a flowchart illustrating steps of a method of determining afocal length of a camera and/or of adjusting a viewing direction in agraphical representation of a pre-operative image of at least a part ofa patient according to an exemplary embodiment of the invention;

FIG. 7 illustrates a step of the method of FIG. 6 .

The figures are schematic only and not true to scale. In principle,identical or like parts, elements and/or steps are provided withidentical or like reference symbols in the figures.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a flowchart illustrating steps of a method of determining afocal length of a camera and/or of adjusting a viewing direction in agraphical representation of a pre-operative image of at least a part ofa patient according to an exemplary embodiment of the invention.

Step S1 comprises providing uncalibrated camera data of a camera,wherein the uncalibrated camera data comprise an image of at least apart of a tracking system, e.g. positioned close to and/or adjacent to aregion of interest of the patient.

Step S2 comprises specifying and/or assuming an initial value of a focallength of the camera, and step S3 comprises specifying and/or assuming aworking distance value of a distance between the camera and the at leastpart of the tracking system.

Further, step S4 comprises calculating a distance value of the distancebetween the camera (and/or a position of the camera) and the at leastpart of the tracking system, e.g. an orthogonal and/or shortest distancebetween the camera and the at least part of the tracking system, basedon the uncalibrated camera data and based on the specified initial valueof the focal length of the camera.

Step S5 comprises calculating a change factor based on the specifiedworking distance value and based on the calculated distance value.Therein, calculating the change factor may, optionally, comprisecalculating a ratio of the specified working distance value and thecalculated distance value. Accordingly, the change factor may correlatewith the ratio of the specified working distance value and thecalculated distance value.

Optionally, step S5 may further comprise comparing the determined changefactor to a clamp factor, wherein the clamp factor is indicative of amaximum allowed value of the change factor. Further, step S5 mayoptionally comprise the step of reducing, e.g. by a predetermined amountor percentage, the change factor if the determined change factor reachesand/or exceeds the clamp factor.

Further, step S6 comprises calculating an adapted value of the focallength of the camera based on the initial value of the focal length andbased on the change factor.

As indicated by the dotted arrow in FIG. 1 , at least steps S4, S5, andS6 may be repeated in an iteration process. Optionally, also one or moreof steps S1, S2, and S3 may be repeated in the iteration process.

Apart from that, step S4 and/or step S5 may, optionally, comprise thesteps of determining a deviation of the calculated distance value withrespect to the specified working distance value and comparing thedetermined deviation to a threshold value, particularly a predeterminedthreshold value, for the deviation of the calculated distance value withrespect to the specified working distance value.

The iteration process, as indicated by the dotted arrow in FIG. 1 , may,for example, be terminated, if the deviation of the calculated distancevalue with respect to the specified working distance value, asoptionally determined in step S4 and/or S5, reaches and/or falls below athreshold value, particularly a predetermined threshold value, for thedeviation of the calculated distance value with respect to the specifiedworking distance value. In other words, the change factor and/or theadapted focal length value may be calculated if, particularly only if,the determined deviation reaches and/or exceeds the threshold value.Otherwise, the iteration process may be terminated.

FIG. 2 shows schematically a medical system 10 according to an exemplaryembodiment of the invention and/or according to the fifth aspect. Thesystem is in its entirety identified by reference numeral 10 andcomprises a camera 12, an uncalibrated camera 12 and/or a camera 12 thatis configured to provide two-dimensional uncalibrated camera data.

The medical system 10 further comprises a computer 14, an electronicdata storage device (such as a hard disc) 16 for storing at least theuncalibrated camera data acquired by the camera 12. The computer 14 maybe coupled to one or both of the storage device 16 and the camera 12 inorder to retrieve and/or process the uncalibrated camera data.

The medical system 10 further comprises a medical device 18, e.g. forcarrying out a medical procedure. The components of the medical system10 have the functionalities and properties explained above and in thefollowing with regard to the fifth and/or any other aspect of thepresent disclosure.

The medical device 18 further comprises a graphical user interface 20.On the user interface 18, a graphical representation of a pre-operativeimage can be displayed and/or visualized.

Particularly, the at least one computer 14 is operably coupled to the atleast one electronic data storage 16 device for acquiring, from the atleast one data storage device 16, at least the uncalibrated camera data.Further, computer 14 is coupled to the graphical user interface 20 ofthe medical device 18. Moreover, the computer 14 is coupled to themedical device 18 for issuing a control signal to the medical device 18for controlling the operation of the medical device 18, e.g. on thebasis of the uncalibrated camera data and/or on the basis of the adaptedvalue of the focal length of the camera 12, as described above and inthe following with reference to the method and/or the first aspect ofthe invention.

FIG. 3 shows a medical system 10 according to another exemplaryembodiment of the invention. If not stated otherwise, the medical system10 of FIG. 3 comprises the same features as the medical system 10 ofFIG. 2 . FIG. 4 shows a part of a tracking system 22 and/or a markerdevice 24 of the medical system 10 of FIG. 3 .

In the embodiment depicted in FIG. 3 , the data storage device 16 andthe computer 14 are integrated in the medical device 18 and/or thegraphical user interface 20. The graphical user interface 20 may bewall-mounted. Further, the computer 14 may be configured to receive theuncalibrated camera data and/or a video signal from the camera 12directly. Alternatively, the uncalibrated camera data may be stored onthe data storage device 16 and retrieved by the computer 14 from thedata storage device 16. The computer 14 may further be configured tocompute the adapted value of the focal length and/or tracking data, aswill be explained in more detail in subsequent figures.

On the graphical user interface 20, a graphical representation 21 of apre-operative image of at least a part of the patient 19 is displayedand/or visualized. In the example shown in FIG. 3 , the pre-operativeimage is a scan of an abdominal region of the patient 19. However, anyother part or body part may be displayed on the graphical user interface20.

Further, the camera 12 comprises a lighting assembly 13, e.g. an arrayof LEDs arranged around the camera 12 and/or a lens or lens systemthereof. The camera 12 may refer to a standard ceiling mounted camera12. The patient 19 is positioned and/or placed under the camera 12and/or lighting 13. Exemplary, an abdominal region of the patient may beaccessible for the user.

The medical system 10 further comprises a tracking system 22 with amarker device 24. The marker device 24 may be arranged on an instrument,which instrument may be guided with a hand of an operator or user, suchthat also the marker device 24 is guided by the hand of the user. Themarker device 24 comprises a plurality of optical markers 26 arranged onan outer surface of the marker device 24. Particularly, the markerdevice 24 comprise one or more surfaces 25, e.g. at least two surfacesand/or at least two substantially flat surfaces 25, wherein on each ofthe surfaces 25 at least one marker 26, preferably a plurality ofmarkers 26, is arranged. The markers 26 may be monochromatic markers 26and/or each of the markers 26 may comprise an optical pattern.

For example, a plurality of markers 26 can be organized and/or arrangedin marker groups, e.g. on each of the surfaces 25. Further, on each ofthe surfaces 25 at least one and/or at least two, preferably at leastthree, for example four to five, markers 26 may be arranged. This mayensure that the operator can move the marker device 24 freely in hishand whilst tracking is still possible in any orientation of the markerdevice 24. On the basis of the detected markers, as described in moredetail in subsequent figures, and on the basis of determination of theadapted value of the focal length of the camera 12, as described aboveand in the following, the medical system 10 can compute a so called poseand/or an orientation 28 of the marker device 24 relative to the camera12. The orientation 28 of the marker device 24 may, for example, referto a direction 28 of a longitudinal axis of the marker device 24, asindicated by the dashed arrow in FIG. 4 .

For detecting the optical markers 26 by means of the medical system 10and/or according to the method of the first aspect of the invention, asdiscussed in more detail in subsequent figures, a data library may beused, which may e.g. be stored on the data storage device 16. Generally,the medical system 10 may be configured to detect a plurality of markers26 at the same time. This may increase a stability of the tracking.

Generally, with the marker device 24 and/or the instrument in hand, theoperator can dynamically adjust a virtual view and/or a viewingdirection, e.g. centred to a center of view, such as the abdominalregion of the patient 19, as will be explained in more detail insubsequent figures.

FIG. 5 shows a flowchart illustrating steps of a method of determining afocal length of a camera 12 and/or of adjusting a viewing direction in agraphical representation 21 of a pre-operative image of at least a partof a patient according to an exemplary embodiment of the invention. Ifnot stated otherwise, the method of FIG. 5 comprises the same steps asthe method of FIG. 1 .

Step S1 comprises providing uncalibrated camera data of the camera 12,wherein the uncalibrated camera data comprise an image of at least apart of a tracking system and/or a marker device 24, e.g. positionedclose to and/or adjacent to a region of interest of the patient.Further, step S1 comprises specifying and/or assuming a working distancevalue of the distance between the camera 12 and at least a part of thetracking system 22, e.g. the marker device 24. Further, an initial valueof a focal length of the camera 12 may be specified and/or assumed. Theinitial value of the focal length may have a first component in a firstdirection and a second component in a second direction, wherein both thefirst and second direction may be orthogonal to an optical axis of thecamera 12. The uncalibrated camera data, the assumed working distancevalue and the assumed initial value of the focal length may then beprovided as input parameters in step S2 for an iteration loop.

In step S3, the uncalibrated camera data may be processed and/oranalysed based on the initial value of the focal length. Further, instep S3, a value for the distance between the camera 12 and the markerdevice 24 is computed and/or derived from the uncalibrated camera datausing the initial value of the focal length.

In step S4, the calculated distance value and the specified workingdistance value are compared, e.g. based on calculating a ratio of thesetwo quantities and/or by subtracting one of the quantities from theother one. Accordingly, a deviation of the working distance value andthe calculated distance value may be determined in step S4. Optionally,this deviation may be compared to a threshold value. If the thresholdvalue is not reached, the iteration process may be terminated and theiteration loop may start again at any of steps S1 and S2, whereinfurther uncalibrated data may be used as input for the next iterationprocess. This is indicated by reference sign S4′ in FIG. 5 .

On the other hand, if the threshold value is reached and/or exceeded,the method or iteration process may continue along route S4″. Therein, achange factor is calculated in step S5, which change factor may be givenas the ratio of the specified working distance value and the calculateddistance value.

Optionally, in step S6 the determined change factor may be compared to aclamp factor, wherein the clamp factor is indicative of a maximumallowed value of the change factor, e.g. per iteration. Further, step S5may optionally comprise the step of reducing the change factor if thedetermined change factor reaches and/or exceeds the clamp factor.

Finally, in step S7, an adapted value of the focal length is determined,particularly an adapted value of the focal length in a first direction(e.g. an x-direction) and a second direction (e.g. a y direction),wherein both the first and the second direction may be transverse and/ororthogonal to each other and orthogonal to an optical axis of the camera12. Accordingly, the adapted value of the focal length may comprise afirst component which may be given by the product of the first componentof the initial value of the focal length and the change factor.Likewise, the adapted value of the focal length may comprise a secondcomponent which may be given by the product of the second component ofthe initial value of the focal length and the change factor.

FIG. 6 shows a flowchart illustrating steps of a method of determining afocal length of a camera and/or of adjusting a viewing direction in agraphical representation 21 of a pre-operative image of at least a partof a patient according to an exemplary embodiment of the invention. Ifnot stated otherwise, the method of FIG. 6 comprises the same steps asthe methods of FIGS. 1 and 5 . FIG. 7 illustrates a step, particularlystep S0, of the method of FIG. 6 .

As illustrated in FIG. 7 , step S0 comprises registering a longitudinalaxis of the patient 19 based on sequentially pointing at least a part ofthe tracking system 22, particularly a marker device 24 of the trackingsystem 22, to at least two longitudinal points 23 a, 23 b on the patient19, wherein the at least two longitudinal points 23 a, 23 b are spacedapart from each other in a direction 19 a parallel to the longitudinalaxis of the patient 19.

Further, step S0 comprises registering a transverse axis of the patient19 based on sequentially pointing at least a part of the tracking system22, particularly a marker device 24 of the tracking system 22, to atleast two transverse points 23 c, 23 d on the patient 19, wherein the atleast two transverse points 23 c, 23 d are spaced apart from each otherin a direction 19 b parallel to the transverse axis of the patient 19.

The registration has the goal to measure the four main directions of thepatient 19 in three-dimensional space. To do so, the operator mayacquire several single points 23 a-d by pointing the marker device 24 tothese points 23 a-d on the surface of the patient 19. Those points 23a-d may then form the main directions of the patient 19. The obtainedregistration may be bound to a patient reference 29 of the trackingsystem 22, which patient reference 29 may be arranged near and/or closeto the patient 19 at a fixed relative position to the patient 19. Thepatient reference 29, in turn, may comprise one or more markers 26, e.g.flat markers 26, which may e.g. be printed on a surface, asschematically shown in FIG. 7 .

Steps S1 to S6 substantially correspond to and/or are identical withsteps S1 to S6 of the method described with reference to FIG. 1 .Further, steps S1 to S6 may further correspond to the steps of themethod of FIG. 5 . To avoid lengthy repetitions, it is referred to FIGS.1 and 5 for a description of steps S1 to S6.

Step S7 comprises detecting one or more optical markers 26 arranged onone or more surfaces 25, e.g. substantially flat surfaces 25, of amarker device 24 of the tracking system 22 based on the adapted focallength value and based on the uncalibrated camera data, as determined instep S6.

Step S8 comprises determining a position of a reference point of themarker device 24, particularly a position of a tip, a corner and/or edgeof the marker device 24, with respect to the camera 12 and/ordetermining an orientation 28 of the marker device 24 of the trackingsystem 22 with respect to the camera 12. Optionally, in step S8,tracking data may be determined based on the detected one or moreoptical markers 26 of the tracking system 22, wherein the tracking dataare indicative of and/or comprise information about the position of thereference point of the marker device 26. Alternatively or additionally,the tracking data are indicative of and/or comprise information aboutthe determined orientation 28 of the marker device 26 with respect tothe camera 12.

Step S9 comprises displaying, on a graphical user interface 20, agraphical representation 21 of a pre-operative image of at least a partof the patient 19 and adjusting a viewing direction of the graphicalrepresentation 21 of the pre-operative image based on the determinedposition of the reference point of the marker device 26 and/or based onthe determined orientation 28 of the marker device 26 with respect tothe camera 12. Therein, the viewing direction of the graphicalrepresentation may be adjusted according and/or corresponding to theorientation 28 of the marker device 26 with respect to the camera 12.

As indicated by dashed arrow in FIG. 6 , the method may also repeatsteps S1 to S8 iteratively. Therein, after finalizing step S8 in oneiteration, further uncalibrated camera data may be provided in step S1of the subsequent iteration, wherein the further uncalibrated cameradata comprise a further image of the marker device 24. Based on thefurther uncalibrated camera data, steps S2 to S6 may be performed, asdescribed above. Further, based on the further uncalibrated camera data,the one or more optical markers 26 of the marker device 24 of thetracking system 22 are detected in step 7, and a further orientation 28of the marker device 26 of the tracking system 22 with respect to thecamera 12 can be determined in step S8.

When steps S1 to S8 are repeated as described hereinabove, anorientation change of the marker device 26 can be determined in step S9,wherein the orientation change is indicative of a change of the furtherorientation 28 of the marker device 26, as determined based on thefurther camera data, with respect to the determined orientation 28 ofthe marker device 26, as determined based on the camera data.

Moreover, the determined orientation change of the marker device 26 maythen be translated in step S9 into a viewing change of the viewingdirection of the graphical representation 21 of the pre-operative image.Therein, the determined orientation change may be translated into theviewing change based on weighting the determined orientation change witha weighting factor, such that the viewing change is increased ordecreased relative to the orientation change.

Finally, the viewing direction of the graphical representation 21 and/ora center of view may be adjusted in step S9, as described above.

Generally, by determining the position of the reference point of themarker device 26 and the orientation 28 of the marker device 26, theuser can adjust the direction or viewing direction of his virtual view(and/or of the graphical representation 21) relative to a region ofinterest of the patient 19, e.g. an abdominal region of the patient 19.By moving, translating and/or rotating the marker device 26 in hand, theviewing direction, which can be centered on a specific part of thepatient, can then be changed interactively by the user.

Further, as described above, by means of the weighting factor, asensitivity of the change in the viewing direction can be adapted. Inthis sense, the weighting factor can control that a normal rotation ofthe instrument can cause a subtle or a strong rotation of the virtualview and/or the graphical representation 21.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art and practicing the claimed invention, from a study ofthe drawings, the disclosure, and the appended claims.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage. Any reference signs in the claimsshould not be construed as limiting the scope.

The invention claimed is:
 1. A computer-implemented method ofdetermining a focal length of a camera, the method comprising: providinguncalibrated camera data of a camera, wherein the uncalibrated cameradata comprise an image of at least a part of a tracking system;specifying an initial value of a focal length of the camera; specifyinga working distance value of a distance between the camera and the atleast part of the tracking system; calculating a distance value of thedistance between the camera and the at least part of the tracking systembased on the uncalibrated camera data and based on the specified initialvalue of the focal length of the camera; calculating a change factorbased on the specified working distance value and the calculateddistance value, the calculating comprising calculating a ratio of thespecified working distance value and the calculated distance value,and/or wherein the change factor correlates with and/or is indicative ofa ratio of the specified working distance value and the calculateddistance value; and calculating an adapted value of the focal length ofthe camera based on the initial value of the focal length and based onthe change factor.
 2. The method according to claim 1, whereincalculating the distance value comprises: determining a deviation of thecalculated distance value with respect to the specified working distancevalue; and comparing the determined deviation to a threshold value forthe deviation of the calculated distance value with respect to thespecified working distance value.
 3. The method according to claim 1,wherein at least the calculating of the distance value, the calculatingof the change factor, and the calculating of the adapted value arerepeated in an iteration process.
 4. The method according to claim 3,wherein the iteration process is terminated, if a deviation of thecalculated distance value with respect to the specified working distancevalue reaches and/or falls below a threshold value for the deviation ofthe calculated distance value with respect to the specified workingdistance value.
 5. The method according to claim 1, further comprising:comparing the determined change factor to a clamp factor, wherein theclamp factor is indicative of a maximum allowed value of the changefactor.
 6. The method according to claim 5, further comprising: reducingthe change factor if the determined change factor reaches and/or exceedsthe clamp factor.
 7. The method according to claim 1, wherein thetracking system comprises a marker device with at least one surface,wherein at least one optical marker is arranged on the surface of themarker device.
 8. The method according to claim 1, further comprising:detecting one or more optical markers arranged on one or more surfacesof a marker device of the tracking system based on the adapted focallength value and based on the uncalibrated camera data; and determininga position of a reference point of the marker device with respect to thecamera; and/or determining an orientation of the marker device of thetracking system with respect to the camera.
 9. The method according toclaim 8, further comprising: displaying, on a graphical user interface,a graphical representation of a pre-operative image of at least a partof a patient; and adjusting a viewing direction of the graphicalrepresentation of the pre-operative image based on the determinedposition of the reference point of the marker device and/or based on thedetermined orientation of the marker device with respect to the camera.10. The method according to claim 9, wherein the viewing direction ofthe graphical representation is adjusted according and/or correspondingto the orientation of the marker device with respect to the camera. 11.The method according to claim 8, further comprising: providing furtheruncalibrated camera data of the camera, wherein the further uncalibratedcamera data comprise a further image of the at least part of thetracking system; detecting the one or more optical markers of the markerdevice of the tracking system based on the further uncalibrated cameradata; determining a further orientation of the marker device of thetracking system with respect to the camera based on the furtheruncalibrated camera data; and determining an orientation change of themarker device, the orientation change being indicative of a change ofthe further orientation of the marker device, as determined based on thefurther camera data, with respect to the determined orientation of themarker device, as determined based on the camera data.
 12. The methodaccording to claim 11, further comprising: translating the determinedorientation change of the marker device into a viewing change of theviewing direction of the graphical representation of the pre-operativeimage.
 13. The method according to claim 12, wherein the determinedorientation change is translated into the viewing change based onweighting the determined orientation change with a weighting factor,such that the viewing change is increased or decreased relative to theorientation change.
 14. The method according to claim 13, furthercomprising: registering a longitudinal axis of the patient based onpointing at least a part of the tracking system to at least twolongitudinal points on the patient, wherein the at least twolongitudinal points are spaced apart from each other in a directionparallel to the longitudinal axis of the patient; and/or registering atransverse axis of the patient based on pointing at least a part of thetracking system to at least two transverse points on the patient,wherein the at least two transverse points are spaced apart from eachother in a direction parallel to the transverse axis of the patient. 15.The method according to claim 14, wherein the camera is a standardoperating room camera; and/or wherein the camera is a two-dimensionalcamera.
 16. A program logic stored in a memory device of a computer thatwhen executed on the computer or when loaded onto the computer, causesthe computer to perform a method comprising: providing uncalibratedcamera data of a camera, wherein the uncalibrated camera data comprisean image of at least a part of a tracking system; specifying an initialvalue of a focal length of the camera; specifying a working distancevalue of a distance between the camera and the at least part of thetracking system; calculating a distance value of the distance betweenthe camera and the at least part of the tracking system based on theuncalibrated camera data and based on the specified initial value of thefocal length of the camera; calculating a change factor based on thespecified working distance value and the calculated distance value, thecalculating comprising calculating a ratio of the specified workingdistance value and the calculated distance value, and/or wherein thechange factor correlates with and/or is indicative of a ratio of thespecified working distance value and the calculated distance value; andcalculating an adapted value of the focal length of the camera based onthe initial value of the focal length and based on the change factor.17. A medical system, comprising: a) at least one computer configured toperform a method including: providing uncalibrated camera data of acamera, wherein the uncalibrated camera data comprise an image of atleast a part of a tracking system; specifying an initial value of afocal length of the camera; specifying a working distance value of adistance between the camera and the at least part of the trackingsystem; calculating a distance value of the distance between the cameraand the at least part of the tracking system based on the uncalibratedcamera data and based on the specified initial value of the focal lengthof the camera; calculating a change factor based on the specifiedworking distance value and the calculated distance value, thecalculating comprising calculating a ratio of the specified workingdistance value and the calculated distance value, and/or wherein thechange factor correlates with and/or is indicative of a ratio of thespecified working distance value and the calculated distance value; andcalculating an adapted value of the focal length of the camera based onthe initial value of the focal length and based on the change factor; b)at least one electronic data storage device storing at least theuncalibrated camera data; and c) a medical device for carrying out amedical procedure on the patient, wherein the at least one computer isoperably coupled with: the at least one electronic data storage devicefor acquiring, from the at least one data storage device, at least theuncalibrated camera data, and the medical device for issuing a controlsignal to the medical device for controlling an operation of the medicaldevice.
 18. The medical system according to claim 17, wherein themedical device comprises: a graphical user interface for displaying agraphical representation of a pre-operative image of at least a part ofthe patient; wherein the at least one computer is operably coupled withthe graphical user interface for controlling a viewing direction of thegraphical representation based on the calculated adapted value of thefocal length of the camera.